Paper manufacture



Patented July 23, 1940 UNITED STATES PAPER MANUFACTURE Louis C. Fleck,Appleton, Wis., assignor to Paper Patents Company, Neenah, Wis., acorporation of Wisconsin No Drawing. Application February 14, 1938,Serial No. 190,419

8 Claims.

The present invention relates to the manufacture of paper from cellulosefibers and more particularly to the production of paper containingground wood fibers and an alkaline filler.

In the manufacture of paper from pulp containing ground wood fibers ithas been known for some time that ordinary alkaline fillers such ascalcium carbonate should not be used when a white sheet is desired.Ground wood, for example, containing all of the organic and inorganicmaterials of natural wood such as lignin, tannins, etc., darkens incolor in an alkaline me dium. Many suggestions have been made in thepast, including means for stabilizing the pH value of alkaline fillers,in the search by previous investigators to find a satisfactory methodwhich would permit the use of an alkaline filler with ground wood in theformation of a paper sheet of high brightness. The prior methods,however, have not been found to be generally satisfactory for in manyinstances, the alkaline filled ground wood papers prepared by thesuggested processes still have a tendency towards discoloration oryellowing while in some cases the addition of acids have destroyed thedesired characteristics of alkaline filled papers. In addition, many ofthe suggested processes were complex in nature, involving critical pHadjustments which are difiicult to control, making the prior methodsunsatisfactory for large scale commercial adaptation. In view of theabove, ground wood has been considerably restricted in use, althoughground wood which is obtained by mechanical grinding processes isrelatively inexpensive compared to the cost of chemically treated woodsuch as sulphite pulp.

The principal object of my invention is to provide a method of makingalkaline filled paper containing ground wood fibers which will be freefrom discoloration.

Another object of my invention is to provide a method of making papersheets of high brightness or whiteness in which the sheets contain analkaline filler and ground wood fibers.

A further object of my invention is to provide a method of usingalkaline fillers and ground wood pulp in the manufacture of paper wherea white sheet is desired that will be adaptable for large scalecommercial utilization.

Other objects will be apparent as the description hereinafter proceeds.

I have discovered that alkaline fillers such as calcium carbonate may besatisfactorily used in the manufacture of paper containing ground woodpulp when the paper contains an aluminum phosphate pigment as anadditional filler. I have also discovered that improved results areobtainable when the pulp or furnish containing ground wood fibers isfirst mixed with an aluminum phosphate pigment or an aluminum phosphatecomplex prior to the addition or use of the alkaline filler. Thealuminum phosphate pigments have an unexpected protective action andexhaustive investigations have shown that the aluminum phosphatepigments, particularly 10 when added to ground wood pulp prior to theaddition of the alkaline filler, in accordance with my preferredprocess, keeps the ground wood from darkening in color in the presenceof the alkaline filler.

Investigations have shown that the unexpected results obtained throughthe use of my invention are not due to pH adjustments, including thelowering of pH value. For example, the addition of free phosphoric acidto ground wood pulp followed by the addition of an alkaline filler suchas calcium carbonate does not produce the desired results. Papercontaining ground wood and made by using free phosphoric acid and analkaline filler is subject to discoloration in manufacture and the finalsheets possess a brightness substantially below sheets containing smallamounts of an aluminum phosphate pigment used in accordance with thepreferred embodiment of the present invention. Although the theory of myinvention is not known, my investigations have shown the aluminumphosphate pigments to possess a peculiar action preventing discolorationof ground wood by alkaline fillers and particularly the calciumcarbonate fillers. 3

The following examples will serve to illustrate the preparation ofaluminum phosphate pigments for use in my invention:

Example I 40 About 600 pounds of sodium hydroxide and about 600 poundsof aluminum hydrate are added to about 290 gallons of water and boiledfor approximately to minutes until the solution is clear. The solutionis diluted to about 720 gallons with water and then added to about 720gallons of water to which separately but at the same time about 1640pounds of '75 percent phosphoric acid diluted to 720 gallons with wateris being slowly added. To the above solution sufficient paper makersalum (aluminum sulphate) is added so that the final solution has a pHvalue of approximately 5. The precipitate formed may be separated byfiltration in the usual manner. In the above example the proalum.

portions on a dry basis are approximately 2 parts alkali hydroxide, 2parts aluminum hydrate, 4 parts phosphoric acid and 2 parts paper makersExample 11 About 558 pounds of 75 percent phosphoric acid diluted with558 pounds of water are mixed with about 720 pounds of iron-freepapermakers alum dissolved in about 720 pounds of water. To

this mixture is added an aqueous calcium hydroxide suspension containingapproximately 100 grams of Ca(OH) 2 per liter of water until the pHvalue has been raised to about 5.0 to 5.2. The calcium aluminumphosphate complex precipitate obtained is an extremely good paperpigment for use in the present invention.

Example III About 975 pounds of '75 percent phosphoric acid and about780 pounds of 95 percent sulphuric acid are mixed with 5800 pounds ofwater. About 585 pounds of aluminum hydrate are added to the above acidmixture which is then heated to a boil for approximately 20 to 30minutes until the aluminum hydrate dissolves. The pH value may beadjusted by adding the solution to about 7800 pounds of an aqueoussuspension of calcium hydroxide containing about 100 grams of calciumhydroxide per liter of water. The use of the mixture of acids appears toform a phosphate-sulphate aluminum complex resulting in a pigmentpossessing unusual protective properties.

It will be apparent from the above examples that throughout thespecification and claims the term aluminum phosphate pigment is intendedto cover not only substantially insoluble aluminum phosphates, but alsovarious other white physical and chemical combinations or complexes ofaluminum and the phosphate radical which are substantially insolubleunder paper making conditions and which might occur under varyingconditions. Thus compounds suitable for use in the present invention mayinclude acid or basic aluminum phosphates, double phosphates as, forexample, the double phosphate of aluminum and calcium; and othermodifications or compositions containing various basic or acid radicalswhich in view of the complex nature of the molecule are difficult toanalyze and assign a definite chemical formula.

Reference is made to my co-pending application, Serial No. 151,456,filed July 1, 1937, which describes in detail the preparation ofaluminum phosphate pigments. For purposes of the present invention ithas been found preferable to precipitate the pigments at pH values of 5to 7, although pigments obtained at lower or higher (e. g., a to 8) pHvalues have been found satisfactory.

The following example will serve to illustrate the present invention:

Example IV Paper made up of.50 percent ground wood and 50 percentbleached sulphite fiber furnish and containing 20 percent by weight ofinorganic filler material consisting of 90 percent calcium carbonate andpercent aluminum phosphate pigment prepared for example by the method ofExample I, the aluminum phosphate pigment having been mixed with theground wood furnish prior to the addition of the calcium carbonate,shows an improvement of approximately 9-10 points in brightness over asheet made from the same furnish containing no filler. Although thepaper above described contains only 2 percent by weight of aluminumphosphate pigment which is used in accordance with the preferredembodiment of my invention, thepaper nevertheless shows an improvementof about 3 points in brightness over paper made with a similar fiberfurnish containing 20 per-- v ordinarily preferred to use about 10percent of aluminum phosphate pigment. The use of less than 5 percentaluminum phosphate pigment results in minor improvements which are notas a general rule of commercial importance. If desired, largerpercentages, e. g., 20 to 30 percent, of aluminum phosphate may be used,although the increasein improvement is not proportional and is in mostcases substantially the same. as'that obtainedusing my preferredpercentage. g

It will be understood that the aluminum phosphate pigments may beprecipitated or formed in the presence of the ground wood fibers, inwhich case. the protecting pigment will be deposited directly on thefibers, or may be separately prepared. and added to the furnish. Ineither case it is preferred in order to obtain the improved brightnessas well as freedom from discoloration that the ground wood fibers bethoroughly mixed with aluminum phosphate pigment prior to theintroduction of the alkaline filler. It will also be understood by thoseskilled in the paper art that the common sizing compositions includingalum, rosin, starch and the like, may be use-d in the manufacture ofpaper in conjunction with the present invention, and in addition thatother non-alkaline filler materials such as calcium sulphite, whichgives a particularly good result, may be employed with the alkaline andaluminum phosphate fillers, if desired.

It will be understood that although in my preferred process the alkalinefiller is added after the addition of the aluminum phosphate pigment,the increase in brightness may be obtained by adding the alkaline fillerand aluminum phosphate in admixture or simultaneously to the pulpcontaining the ground wood fibers. Discoloration may also be preventedor retarded when the aluminum phosphate pigment is added after thealkaline filler, although it is preferred in this case to add thealuminum phosphate complex immediately or shortly after the addition ofthe alkaline filler.

It will also be understood that my invention includes paper containingvarious percentages of ground wood, e. g., 10 to 90 percent ground wood.I have found that paper containing about equal proportions of groundwood and sulphite pulp (pulp cooked with bisulphite, sulphur dioxide,etc.) to be particularly adaptable for use in my invention. It willlikewise be understood by those skilled in the art that the termalkaline filler includes calcium carbonate, the calciumcarbonate-magnesium carbonate and hydroxide complexes. etc.

Numerous other applications of my invention will doubtless suggestthemselves to those skilled in the art without departing from the spiritof my invention. Hence, I do not wish to be limited to the specificdetails or embodiments disclosed herein, but intend that the scope of myinvention shall be determined from the appended claims, which should beinterpreted as broadly as the state of the art will'permit.

I claim:

1 In a method of making paper from cellulose fibers which includessubstantial amounts of ground wood fibers and an alkaline filler as twoof its essential ingredients, the improvement which consists in addingan insoluble aluminum phosphate pigment to said cellulose fibers priorto the use of the alkaline filler in making said paper, the proportionsof ingredients employed in said method being such that said pigmentmakes up at least about 5 per cent of the total filler material in saidpaper.

2. In a method of making paper from cellulose fibers which includes notless than about 10 per cent ground wood fibers and a substantial amountof calcium carbonate filler as two of its essential ingredients, theimprovement which consists in mixing an insoluble aluminum phosphatepigment with said ground wood fibers prior to the addition of thecalcium carbonate filler to said cellulose fibers, the proportions ofingredients employed in said method being such that said paper containsat least 10 per cent filler material and said pigment makes up at leastabout 5 per cent of the total filler material insaid paper.

3. In a method of making an alkaline filled paper from a pulp furnishcontaining 10 to 90 percent ground wood fibers, the improvement whichconsists in adding an aluminum phosphate pigment to said ground woodfibers prior to the addition of the alkaline filler to said furnish, theproportions of ingredients employed in said method being such that saidpaper contains at least 10 per cent filler material and said pigmentmakes up at least about 5 per cent of the total filler material in saidpaper.

4. The step in the method of making paper from a furnish containingsubstantial amounts of ground wood fibers, sulphite fibers, and analkaline filler as three of its essential ingredients, the improvementwhich consists in mixing an aluminum phosphate pigment with said groundwood fibers prior to the addition of said sulphite fibers and saidalkaline filler to the furnish containing said ground wood fibers, theproportions of ingredients employed in said method being such that saidpaper contains at least 10 per cent filler material and said pigmentmakes up at least about 5 per cent of the total filler material in saidpaper.

5. Paper containing a substantial amount of ground wood fibers and analkaline filler as essential ingredients and an aluminum phosphatepigment, the total filler in said paper being made up of at least about5 percent of said aluminum phosphate pigment, said paper being free fromdiscoloration ordinarily present in alkaline filled papers containingground wood fibers.

6. Paper containing sulphite pulp and not less than about 10 percentground wood fibers and filled with calcium carbonate and an aluminumphosphate pigment, the total filler in said paper being at least 10percent of the weight of said paper and being made up of at least about5 to 10 percent of said aluminum phosphate pigment.

7. Paper containing sulphite pulp and 10 to 90 percent ground woodfibers and filler material consisting essentially of an alkaline filler,and an aluminum phosphate pigment, the total filler material being atleast about 10 percent of the weight of said paper and the aluminumphos-- phate pigment being at least about 5 percent of the total fillermaterial.

8. Paper containing about equal proportions of chemical pulp and groundwood fibers and filled with filler material containing a majorproportion of calcium carbonate and a minor proportion of an aluminumphosphate pigment, said paper at least 10 percent filler materialcontaining at least about 1 percent based on the weight of the paper ofsaid aluminum phosphate pigment and said pigment making up at leastabout 5 per cent of the total filler material in said paper.

LOUIS C. FLECK.

. CERTIFICATE OF CORRECTION; Patent No. 2,208,571 July 25, 191 0.

' LOUIS C.- FLECK. 7

It is hereby certified that error appears in the printed. specificationof the above numbered patent requiring correction as follows: Page 1,second column, line h.6, after the word added insert "slowly-" page 5,

second column, line L2, claim 8, after "paper" insert --containing--;and

that the said Letters Patent should'be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this let day of October, A. D. 1914.0.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

